Quantitative and Molecular Genetic Variation in

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Quantitative and Molecular Genetic Variation in Captive Cotton-Top Tamarins (Saguinus oedipus) Author(s): James Cheverud, Eric Routman, Cashell Jaquish, Suzette Tardif, Gloria Peterson, Natasha Belfiore and Lisa Forman Source: Conservation Biology, Vol. 8, No. 1 (Mar., 1994), pp. 95-105 Published by: Wiley for Society for Conservation Biology Stable URL: http://www.jstor.org/stable/2386724 Accessed: 05-06-2018 21:55 UTC JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://about.jstor.org/terms

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Quantitative and Molecular Genetic Variation in Captive Cotton-Top Tamarins

(Saguinus oedipus) JAMES CHEVERUD ERIC ROUTMAN

CASHELL JAQUISH Department of Anatomy & Neurobiology Washington University School of Medicine St. Louis, MO 63110, U.S.A.

SUZETTE TARDIF Marmoset Research Center

Oak Ridge Associated Universities Oak Ridge, TN 37831, U.S.A.

GLORIA PETERSON Department of Epidemiology School of Hygiene and Public Health The Johns Hopkins University 615 N. Wolfe Street

Baltimore, MD 21205, U.S.A.

NATASHA BELFIORE* LISA FORMANt Department of Zoological Research National Zoological Park Smithsonian Institution

Washington, DC 20008, U.S.A.

Abstract: Most genetic surveys of captive and endangered Variacion genetica molecular y cuantitativa en los Pinches populations are carried out with single gene characters bearcautivos (Saguinus oedipus) ing no direct relationship to life history or other features for which genetic variation needs to be maintained. QuantitaResumen: La mayoria de las evaluaciones geneticas depotive genetic estimates of heritable variation for life-history blaciones en peligro se llevan a cabo usando caracteres determinados por un gen unico y que no tienen una relacion * Current address: Department of Zoology, University of Florida, directa con la histora de vida u otra caracteristica para la Gainesville, FL 32610, US.A cual es necesario mantener variabilidad genetica Estimat Current address: Cellmark Diagnostics, Germantown, MD 20876, US.A dores geneticos cuantitativos de varaci6n heredablepara caAddress correspondence to j Cheverud Department of Anatomy & racteres de historia de vida podrian ser una forma mas diNeurobiology, Box 8108, Washington University School of Medicine, recta y apropiada de medir la variacion genetica para al660 S Euclid Avenue, St. Louis, MO 63110, US.A Paper submitted February 20, 1992; final manuscript accepted Au- gunos prop6sitos conservacionistas. Mas aun, resultados te6ricos y empiricos recientes indican que la variaci6n gegust 21, 1992. 95 Conservation Biology, Pages 95-105 Volume 8, No. 1, March 1994


96 Genetic Variation in Cotton-Top Tamarins Cheverud et al.

traits may be a more direct and appropriate netica medida enmeasure estos dos niveles of poria ge-no concordar. Nonetic variation for some conservation purposes. Further- en 41 loci de aloenzsotros analizamos la heterocigosidad more, recent theoretical and empirical indicate thaten el Pinche cauimas yresults la heredabilidad del peso corporal genetic variation measured on thesetivo two levels may not be (Saguinus oedipus) del Marmoset Research Center, Oak concordant. We analyzed heterozygosity at 41Universities, allozyme Ridge Associated a los loci efectos de comparar estos and heritability for body weight in dos captive niveles de cotton-top variacion genetica tamLos Pinches son una espearins (Saguinus oedipus) from the Marmoset Research Center cie en gran peligro de extinci6n nativa de Colombia En la of the Oak Ridge Associated Universities inmuchos order to compare actualidad, animales residen en facilidades dedicathese two levels of genetic variation.das Cotton-top are Se utilizaron a la investigacin ytamarins enparques zool6gicos. de 106 animales en la evaluacion a highly endangered species native un tototal Colombia Many ani- de aloenzimas mals currently reside in research facilities and zoological mientras que datos sobre 364 animales contribuyero parks. A total of 106 animals were used thecuantitativo isozyme surestudio in genetico del peso corporal. Enconvey, while data on 364 animals contributed to the quantitramos una heterocigosidad promedio muy baja (H = 1%) tative genetic study of body weight. We found very en esta colonia El peso a corporal fuelow moderado y significativamente heredable (h2 = 35%). Esta heredabilidad esta average heterozygosity (H = 1%) for this colony. Body weight was moderately and significantly heritable (h2 = dentro de los rangos normales para las poblaciones natu35%). This heritability is within the normal range for natrales de animales. El descubrimiento de niveles biol6gicaural animal populations. The finding of biologically signifmente significativos de heredabilidad en unapoblacion con icant levels of heritability in a population with abnormally niveles anormalmente bajos de heterocigosidad de aloenzilow allozyme heterozygosity illustrates the point that low mas ilustra el argumonto de que bajos niveles de heterocilevels of allozyme heterozygosity should not be taken as an gosidad de aloenzimas no deverian tomarse como un indiindication of overall lack of genetic variation in important cador de la falta de variaci6n genetica total en caquantitative characters such as life-history traits. Genetic racteres cuantitativos importantes, tales como caracteres de variation required for adaptation of species to future envi- historia de vida La variaci6n genetica requerida para la ronmental challenges can exist despite low levels of enzyme adaptaci6n de la especie a desafios ambientales futuros heterozygosity. puede existir a pesar de bajos niveles de heterocigosidad de aloenzimas.

Introduction

ferred measure of genetic variation, and hetero ties below about 3% are considered low for prim The level of genetic variation in captive and wild pop- et al. 1986). However, genetic variance (Forman ulations of endangered species is of concern because specificof molecular phenotypes themselves is of li recton interest. Rather, the molecular markers are co the potentially deleterious effects of inbreeding the ability of a population to adapt to novel and ered changing to be a representation of genetic variation environments through natural selection (Frankel genome andas a whole. Soule 1981; Soule 1986; Vrijenhoek 1989). Genetic sur- phenotypes of direct concern in endan Often, veys of some natural and captive populations of endanpopulations are quantitative in nature, such as characters or disease resistance. These p gered species, including cheetahs (O'Brien et history al. 1983), elephant seals (Bonnell & Selander 1974), and golden types are inherited through the combination of lion tamarins (Forman et al. 1986), have found low levgenes, each typically of relatively small effect. G els of protein polymorphism. This raises concern that in quantitative characters is measured variation population bottlenecks have reduced genetic additive variation genetic variance, or heritability, using to critical levels, limiting future evolutionary adaptabiltative genetic approaches (Falconer 1981). The l ity and reducing fecundity and survivorship due to inisozyme heterozygosity may not be a very usefu breeding depression. These findings have suggested sure of the level of genetic variation in quantitativ acters (Hoffman et al. 1984; Lewontin 1984; Lan that effective population sizes must be kept at a relaBarrowclough 1987; Lande 1988). tively high level to maintain reasonable amounts of genetic variation (Franklin 1980; Lande & Barrowclough The evolutionary dynamics of single-locus poly 1987). phisms and quantitative genetic variation in sm ulations, Genetic surveys of endangered populations have beenor of population bottlenecks, are not ne ily inherthe same. Lande and Barrowclough (1987) sho carried out using molecular genetic phenotypes ited in a Mendelian fashion (O'Brien et al. 1983; Forman the effective population size necessary for main et al. 1986; Gilbert et al. 1990; Templeton et reasonable al. 1987). amounts of genetic variation is much Heterozygosity, the average proportion of heterozygous and that recovery time after a bottleneck is much

individuals per locus (Weir 1990), has beenfor thesingle-locus prevariants than for quantitative char

Conservation Biology Volume 8, No. 1, March 1994


Cheverud et al. Genetic Variation in Cotton-Top Tamarins 97 Furthermore, there are some distinct differences in the Because single-locus variants and quantitative genetic

behavior of single-locus variants and quantitative gevariation may react differently to demographic pronetic variation at a population bottleneck. Additive gecesses, quantitative genetic surveys of endangered and netic variation, in contrast to heterozygosity, has actucaptive populations may be an important adjunct to ally been observed to increase after a population now traditional molecular surveys, as suggested by bottleneck for morphological characters in house flies Lande (1988; Lande & Barrowclough 1987). We present (Bryant et al. 1986a, 1986b; Bryant & Meffert 1988, the results of a survey of genetic variation at protein loci 1990; McCommas & Bryant 1990). While additive ge- and for a quantitative character in the captive colony of netic variation increased after population bottlenecks in cotton-top tamarins (Saguinus oedipus) maintained at this experiment, the increase was accompanied by a the Marmoset Research Center, Oak Ridge Associated reduction in mean viability and body size, indicating Universities. We estimate the genetic variance of body

inbreeding depression (Bryant et al. 1986a, Hedrick size using quantitative genetic methods and estimate the

1987). average heterozygosity of single-locus enzyme variants. In order to understand the effects of population bot- Cotton-top tamarins are thought to be rare in the wild tlenecks on quantitative genetic variation, it is necessary (Savage 1990), with only several hundred remaining in to consider the different types of genetic variation in- Colombia. Approximately 1500 cotton-top tamarins cluded in quantitative genetic theory. The total geno- currently reside in research colonies and zoological typic variance, or differences between individuals due parks (Tardif & Colley 1989; Savage 1990); where they to differences in their genes, is composed of three parts. have been successfully bred (Clapp & Tardif 1985; The additive genetic variance represents the statistically Snowdon et al. 1985; Price & McGrew 1990;Johnson et independent and additive effects of alleles on pheno- al. 1991). types. The dominance variance is due to the effect of intralocus allelic interactions on the phenotype. Finally, Materials and Methods the epistatic variance is due to the effect of interlocus

allelic interactions on phenotypes (Falconer 1981). The colony of cotton-top tamarins at the Marmoset Re-

While the additive genetic portion of the total genotypic

search Center, Oak Ridge Associated Universities, was begun in 1961 by importing animals from the wild. Imphenotypic similarity among relatives, precise estimates portation stopped in 1976 when the cotton-top tamarin of dominance and epistatic variance are very difficult to was classified as an endangered species by the United obtain (Falconer 1981). The total genotypic variance States. Only 80 animals were imported prior to 1972, 58 and the proportional contributions of its components animals between 1972 and late 1974, and then 263 andepend, in part, on allele frequencies at the large numimals from late 1974 through the end of 1976. The only ber of loci that contribute to variation in the phenotype. major addition to the colony after 1976 was the transfer Only the additive genetic effects of genes can be inherof 50 animals from the Rush Presbyterian-St. Luke's ited in many organisms, because each parent passes only Medical Center colony in 1981. Of these more than 450 one of its pairs of alleles to an individual offspring and animals, only about one third produced laboratory-born alleles at separate loci assort independently (a minor offspring. Animal husbandry is described in Clapp and portion of the epistatic effects can also be inherited by Tardif (1985). offspring from parents). Furthermore, only heritable, or additive genetic, variation can serve as a basis for evoSurvey of Single Locus Genetic Variants lutionary adaptive responses to selection. Changes in allele frequencies in small populations, or Blood samples were obtained from 106 animals repredue to founder effects, can result in dominance and epi- senting all the continuing genetic lineages in the colony static variance being converted into heritable additive and extracted using methods published elsewhere variance, thus enhancing the evolutionary potential of a (O'Brien 1980). All animals were surveyed for allozyme population (Bryant et al. 1986a, 1986b; Goodnight variability at 21 loci. Thirty-six animals were repre1987, 1988; Bryant & Meffert 1988, 1990; Carson & sented by both red cell extracts and extracts derived Wisotzkey 1989; McCommas & Bryant 1990). This oc- from fibroblast cell lines in order to confirm genotypes curs even though total genotypic variation and average obscured by blood chimerism (Benirschke et al. 1962), single locus heterozygosity declines (McCommas & permitting a comparison of an additional 13 loci for Bryant 1990). It should be noted that whether or not between 80 and 100 animals. The fibroblast extracts conversion of nonadditive genetic variance was the were also used to examine allozyme patterns for an cause of increased additive genetic variance in Bryant's ditional 5 loci not expressed in red blood cells. Appro house fly experiments (Bryant et al. 1986^a 1986b) is imately 60 plasma samples were screened for serum albumin and serum transferrin variants. still open to question (Hedrick 1987; Lynch 1988). variance can be estimated relatively simply using the




Histochemical staining procedures are as describ The presence of blood chimerism in cotton-top tamO'Brien (1980) andusual Harris alloand Hopkinson (1976 arins presented a particular challenge to the cell and fibroblast and extracts were analyzed on Bu zyme survey based on blood cells. Tamarins marvertical electrophoresis mosets are unusual among primates in that theysystems typi-using 12% starch trostarch, Connaught and/or Sigma Chemical Co. cally give birth to twins. Before birth, the twin placentas proteins analyzedthe on 4.75% acrylamid are partially fused so that bloodrum cells passwere between using a (Benirschke Bio-Rad 220 gel system. twins, resulting in blood chimerism et al. 1962). Blood obtained from any given tamarin often also contains cells from its twin. For this reason an al-

Survey of Quantitative Genetic Variation

ternative tissue, fibroblasts, was also used in the allozyme survey.

BODY WEIGHTS

The electrophoretic conditions used to examine the 41 structural gene loci surveyed here are shown in Ta-Body weight data were collected from a variety of colble 1. Many loci (about 68% ) were analyzed using moreony records. These include the veterinary records, than one buffer condition in order to best reveal varirecords collected prior to bleeding the animals for reability. When sample volume permitted, samples weresearch purposes, and a series of weights collected for also analyzed in duplicate in each buffer system. Onlycolony maintenance purposes. Each of these weight records was scored for reliability on a three-level scale. variants that could be confirmed by pedigree analysis were scored as nolvmornhic. Level 1 was for weights taken on animals when they Table 1. loci examined by electrophoresis in cotton-top tamarins (Saguinus oedipus).

Gene

IUB/IUP

Buffer

Sample

Enzyme Symbol Account No. Tissue* System** Size Acid phosphatase I ACPI 3.1.3.2 RBC TC/TEB >100 Adenosine deaminase ADA 3.5.4.4 RBC TC/TEB >100

Adenylate kinase AK1 2.7.4.3 RBC TC/TEB >100 Carbonic anhydrase 2 CA2 4.2.1.1 RBC TC/TEB >100 Esterase (umbelliferyl) EsU 3.1.1.1 RBC TC/TEB >100 Esterase (aL-napthyl acetate) Esoa 3.1.1.1 RBC/F TC/TEB >100 Glutamate pyruvate transaminase GPT 2.6.1.2 RBC/F TC >100 Lactate dehydrogenaseA LDHA 1.1.1.27 RBC TC >100 Lactate dehydrogenaseB LDHB 1.1.1.27 RBC TC >100 Malate dehydrogenaseI MDHI 1.1.1.37 RBC TC/TEB >100 Peptidase A PEPA 3.4.11 RBC/F TC/TEB >100 Peptidase B PEPB 3.4.11 RBC/F TC/TEB >100 Peptidase C PEPC 3.4.11 RBC/F TC/TEB >100 Peptidase D PEPD 3.4.11 RBC/F TC/TEB >100 Phosphoglyceromutase PGAM 2.7.5.3 RBC/F TC/TEB >100 Phosphogluconate dehydrogenase PGD 1.1.1.44 RBC/F TC/TEB >100 Triosephosphate isomerase TPI 5.3.1.1 RBC TEM >100 Inorganic pyrophosphatase PP 2.7.5.1 RBC TEM >100 Glucose phosphate isomerase GPI 5.3.1.9 RBC TC/TEB >100 Hemoglobin Hb RBC TC/TEB >100 Nucleoside phosphorylase NP 2.4.2.1 RBC TC/TEB >100 Diaphorasel DIA1 1.6.*.* RBC/F TC/TEB >75 Diaphorase4 DIA4 1.6.*.* RBC/F TC/TEB >75 Glucose-6-phosphate-dehydrogenase G6PD 1.1.1.49 RBC TC/TEB >75 Glutathione reductase GSR 1.6.4.2 RBC/F TC/TEB >75

Phosphoglucomutase3 PGM3 2.7.5.1 F TC/TEB >35 Phosphoglucomutasel PGM1 2.7.5.1 RBC/F TC/TEB >75

Aldolase A ALDA 4.1.2.13 RBC TC >50 Glutamate oxaloacetate transaminase GPT 2.6.1.2 RBC TC/TEB >50

Mannose phosphate isomerase MPI 5.3.1.8 F TC/TEB >35 Malic Enzyme I MEI 1.1.1.40 F TC >35 Hexokinase

Catalase

1

HK1

CAT

2.7.1.1

1.11.16

RBC/F

RBC

TEB

TEB

>35

>45

Isocitrate Dehydrogenase IDH 1.1.1.42 F TC >10 Transferrin

Tf

P

TG

>60

Phosphoglucomutase 2 PGM2 2.7.5.1 F TC >35 Albumin * **

RBC

=

Alb

red

Buffer

--

blood

systems

TG

cell are

Conservation Biology Volume 8, No. 1, March


>60

extract

as

1994

repor

Cheverud et al. Genetic Variation in Cotton-Top Tamarins 99

samediseases holds true for sex. Towere the extent that the were ill and under veterinary careThe for that likely to affect body weight, suchgenetic as colitis. Level 2 was correlation of body weight as expressed i

for weights taken on animals under veterinary care due males and females is less than one due to genotype b to a traumatic injury or other condition not likelyestimates to sex interaction, heritability will be biased severely affect body weight. Finally, was correlations for downwards.level Even if3genetic across enviro weights not associated with treatment but for ments and sexes aretaken one, differences in the level of g other purposes. Pregnant females weighed. neticwere variancenot expressed in different environments a Weights were recorded at 10-gram Only adult sexesintervals. results in an observed genetic variance estima pooled across environments weights, animals over 2.5 yearsthat of isage in this species, and sexes. were included. After preliminary analyses all weight records with reliability level 1 were excluded ESTIMATION OF GENETIC VARIANCE from the analyses, leaving a total of 364 individuals in the sample. The 364 animals with body weight records ultimately Individual animals often had several weights, up to derive from 57 imported males and 47 imported fefive, recorded in the colony records. Many of these remales, so that the sample analyzed here was derived peat weights were from 62 tamarins measured repeatfrom approximately 100 animals. Imported animals are edly over a five-month period. The repeatability of these presumed to be unrelated to one another. There is a weight measurements was very high (repeatability = high variance in the contribution of these imported in95% ), although this may be an overestimate of the redividuals to the laboratory-born generations, so that the peatability for all the records included here. When anieffective number of founders is likely to be less than mals had multiple weights recorded, the most reliable 100. The total sample is derived from 31 independent (the highest level) weight was chosen. If there were genealogies ranging in size from 2 to over 80 individuseveral weights at the same level of reliability and varyals. Eighty-five animals in the sample were not known to ing by less than 10% of their mean, the average weight be related to any other tamarins with measured body was used for the analysis. weights. Most of these animals were imported in the Weight records were classified by sex, level of reliearly 1970s and never bred. The colony is managed to ability, and whether the animal was wild- or laboratoryavoid inbreeding (Clapp & Tardif 1985). born (referred to as environment). Analysis of variance Genetic variances and heritabilities were estimated was used to detect the effects of sex, reliability code, using maximum likelihood methods (Konigsberg and environment on adult body weights. After analyses Cheverud 1992). If body weight observations on a sa of these three covariates, variation in means and variple of related individuals is multivariate normally d ances among classes were removed from the data so that tributed, then the log-likelihood of the observed dat each group had the mean and variance of wild-born adult males with weights recorded at reliability level 3. ln(LK) = -(/2)(x - t1)'V-1(x,u) This correction was performed sequentially, -first for re- ln(2rr), (2) ( /2)lnVl - (N/2) liability, second for environment, and finally for sex, where V is the phenotypic variance/covariance matrix using the following equation: among relatives, x is the vector of body weights, and JL is a vector of the trait's mean value (Hopper & Mathews corrected weight = [(original weight - ,l) 1982). Using the results of quantitative genetic theory, (S2/s1)] + L2 (1) the phenotypic variance/covariance matrix among relativess(V) is a function the additive genetic variance where , refers to mean body weight, refers to of the (sa2), the environmental variance (se2), and the strength standard deviation, the subscript 1 refers to the category of genetic relationships among the individuals (Oij): being adjusted, and subscript 2 refers to the reference

category. Analyses were also performed on logarithmic V = 2 sa2 0 + I se2, (3)

and cube-root transformations of body weight but, since

the results were essentially identicalwhere to those I is the obtained identity matrix and 0 is a m

on the untransformed scale, only the untransformed pected additive regenetic covariances among sults are described here.

or numerators of Wright's coefficient of Obtaining heritability estimates for animals raised in example, 0i is (1/2) for parents and of For two distinct environments assumes that the genetic cor(/4) for half-sibs, given no inbreeding. Do relation of body weight as expressed in the two enviepistatic genetic variance are largely subs ronments is one. This is the same as assuming no genoenvironmental variance term. In order to maximum likelihood estimates of ,I, sa2, type by environment interaction for body weight across the wild and laboratory environments. To the extent values were iteratively adjusted until the l given above is maximized using a search p that genotype by environment interaction does exist, the heritabilities obtained will be biased downwards. vised by Lalouel (1979). Heritability is defi




proportion of the total variance (sa2 + se2) due to hertranslational change. Both polymorphic loci meet itable differences (sa2). The analysis was expectations carried(Table out Hardy-Weinberg 2). usAverage hetis approximately 1%. ing a modified version of the erozygosity MAXLIKH2 program obtained from Lyle Konigsberg (Konigsberg & Cheverud 1992). Quantitative Genetic Analyses The parameterization of the phenotypic variance/ Each of the 3 three covariates significantly affects body covariance matrix given in Equation involves the assize (Table 3). As mentioned above, reliability sumption that environmental effects are randomly dis- level 1 were removed fromIn the analysis but levels 2 and tributed in relation to family records membership. general, 3 are still significantly different, with the most reliable food and water are available ad libitum in the colony weights 0.26 within-group standard deviation units (Clapp & Tardif 1985). However, it is possible that faabove the level 2 records. Environment and sex also had milial environmental factors could cause phenotypic significant effectsare on adult body weight, similarity among relatives. The animals raised in alaboratory-born animals being 0.60 standard deviations larger than wild family setting with the mother, father, and usually a set born animals, and females being 0.19 standard deviaof older siblings, all of whom help care for and hand feed tions larger than males. Variation among the infants (Tardif et al. 1992). Nongenetic differences animals for these three covariates was removed, as described above.

in family social dynamics could lead to differences in The corrected data distribution was not significantly difgrowth and could affect adult body weight. The data ferent from normal at the 0.05 level using the Lilliefors available for this colony does not allow these potential test (Wilkinson 1989). effects to be separated from heritable genetic effects. In additive genetic variance body weight was most mammals, about 10% of the The total variation infor adult 1376.26 g2, resulting in a heritability of 35%. The addibody weight is due to familial environmental effects tive genetic variance (and heritability) significantly (Cheverud 1984). Given the genealogical structure isof different from zero at a level exceeding 0.00001 the data used here and estimates from mammals gener- using the chi-square test for likelihood ratios. The 95% conally, the heritability estimates reported may be biased fidence limit for this heritability estimate covers the upwards by about 3-7%. range from 25-46%.using Heritability also measured sepStatistical significance was determined a was likeliarately using relatedness through males alone and again hood ratio test comparing the likelihood of the model through females alone. Heritability estimated with heritability fixed at 0 to the model that estimatesthrough the sires is 54% (SE = 0.068), while heritability estiheritability within the 0-to-1 range. Standard errors for mated through the dams is 26% (SE = 0.091). Both are the heritability estimates are also available from the likelihood procedure.

statistically significantly different from zero at the 5%

Results

overlap, indicating that even though they are quite disparate, they are not significantly different from each other. At any rate there is no evidence for a maternal

Single-Locus Variants

level. The 95% confidence intervals for these estimates

effect on body weight in this colony. If anything, there

may be some surveyed. paternal effect related to the role of the Table 1 describes the 41 enzyme loci Only father in rearing infants. two of the loci (PGM 3 and PGD) showed genetic variability, resulting in a 5% level of polymorphism (percent of loci with more thanDiscussion one allele present). Although the polymorphism could be seen using either Locus obtained Polymorphisms using the buffer system, clearest resultsSingle were tris-citrate system for both PGD and PGM 3. Protein polymorphism wasBlood observed chiin only two of the

merism was evident when fibroblast extracts and red

41 loci surveyed in the ORAU cotton-top tamarin colcell extracts for the same animal were compared with ony, PGD and PGM 3. Variability was previously reits twin's phenotype. Twin's phenotypes appeared in ported for one of these loci (PGD) when approximately varying strength in individual's red cell extracts. The shadow bands caused by twins were absent in the fibroTable 2. Allele frequencies and significance test for deviation blast extracts. All PGD phenotypes were confirmed from by Hardy-Weinberg expectations in the two polymorphic loci; pedigree analysis, whereby twins with different genoallele A is the slowest migrating, most electropositive allozyme. types were shown to be consistent in their patterns of Locus N Allele A Allele B H X2 (1 df) inheritance. An esterase visualized with an alpha-napthyl

PGM 3 36 0.08 0.92 0.15 0.30* acetate stain also appears to be polymorphic, but this PGD 98 0.30 0.70 0.42 0.06* observation could not be confirmed by the pedigrees * availab:le :fo:r anLalysis and mray be due to post-

Not statistically significant at the 0



Cheverud et al. Genetic Variation in Cotton-Top Tamarins 101 Table 3. Means and standard deviationssample. of the covariates: Giventhree the highly endangered status of wild cotreliability, place of birth, and sex on body (all ton-topweights tamarin populations, we may never know what measurements are in grams).

levels of genetic variation exist in the wild. Thus, we can

Covariate Class Mean SD N Prob.

only judge the observed level of heterozygosity in the

Reliability 2 459.5 56.7 112

captive cotton-top tamarins as low relative to other pri-

3 474.9 61.0 240 0.001

mate species.

Birthplace Wild 451.0 43.7 113

Lab 483.4 63.4 239 0.001

Sex

M

451.4

62.1

181

Body Weight Heritability

F 473.0 57.3 171 0.020

Despite the low heterozygosity for structural gene loci, there is a moderate, statistically significant heritability 20 animals, including six wild-caught for body weight in the cotton-top colony. We have no knowledge tamarins, were surveyed by Nagai of levels etofal. heritable (1986). variation These for body weight workin wild cotton-top tamaringene populations and are(Shimaoka not likely to obers analyzed a total of 16 structural loci

et al. 1984; Nagai et al. 1986). tain suchNagai data given theet highly al. endangered (1986) status of also the

report polymorphism for an species. esterase Therefore, werevealed must compare the with observed allevel pha-napthyl acetate stain. This of genetic may variationbe to that similar found for morphological to the variability we observed forcharacters thisinlocus in our sample. animal populations generally. A heritability However, we were unable to esterase polyof corroborate 35% is within the normal range for morphological morphism by pedigree analysis, characterswhereas in natural populations, PGDfalling and at about PGM the 30th percentile ofthrough the distribution of heritabilities for 3 variation segregated appropriately families. Watkins and his colleagues morphological (Watkins characters in et endotherms al. 1990a, compiled by 1990b, 1991) have also reported Mousseau and limited Roff (1987). It diversity seems likely that there in is molecular phenotypes in cotton-top tamarins. They currently a reasonable level of genetic variation in this found that nucleotide sequences population and among that its continued expressed managementmacan be jor histocompatibility complex directed towards (MHC) maintainingclass the existing I variation. genes were less diverse in captive cotton-top tamarins in Without knowledge of the pre-existingthan levels of geother mammalian species. Watkins netic variation in the and wild, Letvin we can only speculate (1991) on the extended these results to the closely-related red-crested specific causes of the relatively low heterozygosity and bare-faced tamarin, S. geoffroyi, normal heritability but found in this cotton-top normal tamarin levels populaof variability in MHC class I genes tion. The effective in other size of the callitrichids, founding population was probably much lower than 100 animals, however, indiincluding saddle-back tamarins (S. fuscicollis), Spix' cating that the population passed through a moderate moustached tamarins (S. mystax), and common marmobottleneck at that time. The disparity between the resets (Callithrix jacchus). for heterozygosity Research and heritability may be due to The heterozygosity of thesults Marmoset Censome combination of the lessabout severe founder effects preter's cotton-top tamarin colony was low, 1%. This is as low as for some other dicted endangered for additive genetic species, variance (Lande such & Barrowas cheetahs (1.3%; O'Brien et al. 1983) the closelyclough 1987) and and to the possibility that additive genetic related lion tamarins (1%; Forman variance may have et increased al. 1986). due to reapportionment Average of dominance andspecies epistatic variance at a bottleneck (Bryheterozygosity for most primate varies from about 2-10%, with nearly all ant et average al. 1986a, 1986b; heterozygosities Goodnight 1987, 1988; Bryant & Meffert 1988, 1990; Carson & et Wisotzkey 1989; Mcexceeding 3% (Forman et al. 1986; Shotake al. 1991). Commas & Bryant 1990) although alternative The low enzyme heterozygosity indicates that the processes popalso be responsiblebottleneck (Lynch 1988). ulation may have undergonecould a moderate durThe difference in heritability estimates through sires ing importation and establishment as a research colony, and it is consistent with a and founder of less dams repottedpopulation here is interesting and suggestive, than 100 individuals. although not statistically significant. Cotton-top and It would appear that the level of polymorphism other and tamarins are unusual primates in that they typically degree of heterozygosity in this captive colony may be give birth to twins, which are then cared for by adult and adolescent males and females in addition to less than that seen in the wild. In a small (n = 10) sample of wild-caught cotton-top tamarins, variability their mother (Sussman & Kinzey 1984; Vogt 1984; T was seen in 6 of the 30 loci examined (Forman et al. dif et al. 1992). Other group members, and especia unpublished data; Savage 1990). The genotypes of indi- the fathers, both carry and feed the young of th vidual animals were consistent with their presumed group, sometimes to a greater degree than the mot pedigrees, indicating that blood chimerism was not the (McGrew 1988; Savage 1990; Tardif et al. 1990; P cause of the high levels of variability found in this small

1992). The young begin weaning at about 8 weeks, afte




of interest, such as body(Savage weight, are not completely which they beg solid food from group members heritable. Theyto are the also directly 1990). This paternal care may be related rela-affected in important by the environment. This can cause difficulties in tively high heritability measuredways through sires, if sires separating genetic inheritance from environmental inare consistent in their behavior towards offspring of the fluences. same and succeeding litters. Even so, this environmental Fortunately, relatively recent advances influence on body weight typically ends by 20 weeks of in the manage-

mentto of captive populations and endangered species age (Savage 1990) and is not likely carry over suband in years quantitative techniques have reduced the stantially into adulthood after two ofgenetic further negative impact of these problems and opened the way growth. for quantitative genetic surveys. Many captive populaBody weight is probably the best readily available, tions of endangered species are now closely monitored overall character for analysis of genetic variation in capdemographically, and this information is collated and tive colonies due to its important role in a wide variety published in studbooks. These studbooks contain the of life-history processes. It is strongly correlated with basic information on genealogical relationship required other life-history variables in mammals (Peters 1983) for quantitative genetic studies. The life history of the but is less affected than fecundity by variation in mananimals, including place of origin and residence, is reagement practices designed to control breeding. Some ported. Moreover, environmental factors such as diet animals may never be bred in an attempt to reduce are more closely monitored and better recorded than overcrowding caused by successful breeding programs they have been in the past. (Clapp & Tardif 1985) and thus would have no record In addition to changes in record keeping, new quanfor this character. Also, many other life-history charactitative genetic techniques, such as the animal model ters are sex-specific, limiting the sample size to half that (Weir et al. 1988) and related maximum-likelihood possible for analyses of body weight. However, body methods such as the one used here (Lange et al. 1976; weight itself is also highly variable throughout life and Shaw 1987; Konigsberg & Cheverud 1992), have been can be affected by adult nutrition and disease. A more developed in animal and human genetics. These apstable body size measure, such as thigh length, would be desirable but much more difficult to collect, and this proaches can simultaneously utilize data from many kinds of relatives, even including inbred individuals, and measure is not currently available in most colony records. do not depend on the classical experimental designs. Instead, the natural genealogical structure of the population is taken into account in estimating genetic variImplications for Conservation Biology

ance. These methods can also control for environmental

factors, such as place of birth or diet, as covariates or by It is apparent that quantitative genetic approaches promodifying the phenotypic variance/covariance matrix vide a powerful tool for surveys of genetic variation in between individuals (see Equation 3) to take account of captive and endangered populations. They can provide information of genetic variation for phenotypes of inter-environmental similarities. These approaches make it est in conservation biology, and these answers are notpossible to account for measured environmental simi necessarily in accord with the findings from surveys of larity among relatives in quantitative genetic studies. single-locus polymorphisms. If quantitative genetic sur- Quantitative genetic methods can be useful in manveys are useful for measuring the level of genetic varia- aging captive populations. Besides quantifying the over tion in important phenotypes, why haven't they beenall level of heritable variation for a trait in a population, carried out?

it is possible to obtain an estimate of the breeding value

(average phenotypic value of offspring produced by First, quantitative genetic surveys have been considmating an individual randomly in the population) of ered more difficult to implement than molecular sureach individual in the population. This breeding value veys. Measures on 30 to 40 loci for 20 to 30 individuals represents the genetic propensities of an individual an are usually considered adequate to measure average hetis used extensively in selective breeding programs erozygosity at structural gene loci (Lande & Barrow(Weir et al. 1988). Even in nonselective management, clough 1987). In contrast, quantitative genetic variance however, breeding values can be used as additional inestimates require relatively large samples of genealogiin choosing unrelated mates so as to control cally related individuals. For large vertebrates, suchformation as unintended changes in mean and variance for quantitamammals and birds, this usually means that accurate tive characters in small populations. records be available over several generations. Second, Hughes (1991) recently suggested that captive breedquantitative genetic estimates have traditionally been ing programs be reoriented with the specific goal of obtained through breeding experiments using indepenmaintaining diversity at MHC loci, despite loss of varident parent-offspring pairs or full- and half-sib families. ability at other loci; he asserts that virtually all non-MHC These experimental designs are not practical for most polymorphisms are neutral. He suggests that lack of captive or endangered populations. Finally, phenotypes



Cheverud et al. Genetic Variation in Cotton-Top Tamarins 103 Bryant, E. H., and L. M. Meffert. 1988. The effect of an experMHC-related variability in cotton-top tamarins may be

population bottleneck on morphological integration responsible for their relatively imental high susceptibility to inin the housefly. Evolution 42:698-707.

fectious disease (Watkins et al. 1990a, 1990b) and implies that their breeding be managed maintain the Bryant, E. H., and L.to M. Meffert. 1990. Multivariate phenotypic

small amount of variation now differentiation segregating in the among bottleneck lines captive of the housefly. Evolu-

population. However, following Hughes's strategy would degrade the genetic variation in body weight reported here and all other life-history characters, as pointed out by Vrijenhoek and Leberg (1991). Variation in life-history characters is not likely to be neutral in either the captive or natural environments and thus should be maintained. If a goal of maintaining evolutionary plasticity is to be pursued in conservation programs

(Frankel & Soule 1981; Vrijenhoek 1989; Vrijenhoek & Leberg 1991), strong selection of any one character or character complex must be avoided. Selection on any specific phenotype will be experienced by unselected characters and loci as genetic drift, thus diminishing already low effective population sizes. The possibility of performing quantitative genetic surveys has been greatly enhanced by current management

practices for endangered populations and by recent advances in quantitative genetic techniques. While such surveys may have larger sample requirements than do traditional protein or molecular markers, their value in uncovering previously undisclosed variability is clear. Quantitative genetic techniques can serve as an important further tool in the genetic management of endangered populations and, with molecular surveys, should help to increase our understanding of genomic variability in threatened species.

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Acknowledgments

static genetic variance. Evolution 41:80-91.

This work was supported, in part, by NSF grant BSR Goodnight, C.J. 1988. Epistasis and the effect of founder 8906041 to J. Cheverud, NIH grant RR-02022 to S. Tar- events on the additive genetic variance. Evolution 42:441diff, and NCI contract N01 CP21004. We also thank the 454. Oak Ridge Associated Universities' Corporation for their support. The animal portion of this study was performed

in ORAU's AAALAC-accredited facility under the auspices of the ACJC.

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I-*) \ i

Conservation Bio Volume 8, No. 1,
